Monohalomaleic esters and monohalofumaric esters are useful in the preparation of pyridine-2,3-dicarboxylic esters which are key intermediates in the production of a class of highly potent herbicidal agents, 2-(imidazolin-2-yl)nicotinic acids, esters and salts. Monohalomaleic esters and monohalofumaric esters are also useful in the preparation of anilinofumarate which is an important intermediate in the manufacture of 2-(2-imidazolin-2-yl)quinoline-3-carboxylic acid herbicidal agents. Descriptions of the use of these important halomaleate and halofumarate compounds in the manufacture of imidazolinyl herbicidal agents may be found in co-pending application Ser. No. 538,861 filed on Jun. 15, 1990 and U.S. Pat. No. 4,904,816.
Representative of the methods used to prepare halomaleic or halofumaric esters from dihalosuccinic esters are those which entail high reaction temperatures, excess quantities of organic solvent and long reaction times such as described in Japan 76 16,406 and Japan 68 29,571.
It is an object of this invention to provide an improved method for the manufacture of monohalomaleic and monohalofumaric esters from dihalosuccinic esters which employs milder reaction conditions and shorter reaction times.